A glaucoma‐associated OPTN polymorphism, M98K sensitizes retinal cells to endoplasmic reticulum stress and tumour necrosis factor α

Abstract

Optineurin/OPTN polymorphism, M98K is associated with normal tension glaucoma in certain populations, and genetic evidence shows its interaction with tumour necrosis factor–alpha (TNFα) polymorphism in causing glaucoma. Endoplasmic reticulum (ER) stress is also associated with glaucoma. We hypothesized that M98K‐OPTN may sensitize retinal ganglion cells to various types of stress. To test this hypothesis, stable clones of a retinal cell line, 661W, expressing either wild‐type (WT)‐OPTN or M98K‐OPTN were generated and examined for their survival under various stress conditions. Compared with WT‐OPTN expressing cells, M98K‐OPTN expressing cells showed significantly lower cell survival and higher activation of caspase‐3 and caspase‐8 upon treatment with tunicamycin (an inducer of ER stress) or TNFα. Levels of ER stress sensors IRE1α, PERK and ATF6 were significantly higher in M98K‐OPTN expressing cells. Tunicamycin treatment resulted in significantly higher induction of ER stress marker CHOP and several other ER stress response genes regulated by IRE1α‐XBP1, PERK‐ATF4 and ATF6 pathways, in M98K‐OPTN expressing cells. Splicing of XBP1 and ATF6 activation was higher in tunicamycin‐treated M98K‐OPTN expressing cells. Increased levels of PERK and IRE1α proteins in M98K‐OPTN expressing cells were dependent on autophagy. Overall, our results show that M98K‐OPTN sensitizes retinal cells to TNFα and ER stress‐induced cell death. We also show that M98K‐OPTN alters ER stress response signalling, which possibly enhances the sensitivity of retinal cells to ER stress. Our results provide support to the hypothesis that M98K‐OPTN may cooperate with other genetic or environmental factors to cause retinal ganglion cell death associated with glaucoma.